FI78641C - Combined packaging film which is impermeable to gases and vapors and consists of two olefin polymer films - Google Patents

Description

1 78641

This invention relates to double films based on olefin polymer films 5, which have good properties in terms of gas and vapor impermeability in the case of containers for packaging and vapors, and which are particularly well suited for manufacture of products.

More particularly, the invention relates to a composite packaging film which is impermeable to gases and vapors and consists of two olefin polymer films, at least one of which is an oriented polypropylene film, the films being joined together with or without gluing and the at least one film being coated with vinyl. and metallized from the surface in contact with the second film. The invention is characterized in that the lacquer consists of a vinylidene copolymer having a content of vinylidene units of more than 75% by weight, or of a polymer mixture containing polyvinyl alcohol having a medium or high degree of hydrolysis.

As is well known, the materials used for packaging require a number of mechanical, aesthetic, impermeability and thermal weldability properties, as well as other properties that are difficult to find together at the same time in films made from a single type of polymer.

For this reason, composite films are generally used, which are made by joining together several films made of different materials. Thus, for example, composite films and laminates consisting of polyolefin films combined with other thermoplastic polymers and / or metal sheets, such as aluminum foils, are known.

Also known are composite films consisting of 2,78641 oriented polypropylene films combined with unoriented films, which are prepared by extruding mixtures of polypropylene and polyethylene or crystalline ethylene-propylene copolymers.

5 IT Application Publication No. 30,637 A / 76, corresponding to U.S. Patent No. 4,211,811 to the same applicant, describes and applies for a patent for composite films consisting of two polyolefin films, one of which is an oriented polypropylene film and at least one of the two films being metallized therefrom. on a surface in contact with the second membrane.

However, the composite films thus prepared, although having excellent mechanical and physico-mechanical properties such as resistance to perforation, weld resistance, heat weldability, etc., are not satisfactory from the impermeability of gases and vapors to applications requiring very high permeability. .

Thus, the present invention relates to films based on polyolefin-20 films which have a high diffusion resistance of gases and vapors while maintaining the mechanical and physico-mechanical properties typical of these composite films.

This and other objects, which will become apparent from the following description, are achieved by a composite film consisting of two olefinic polymer films, joined together with or without an intermediate adhesive, in which at least one is an oriented polypropylene film, and at least one is coated with a lacquer 30 which acts as a gas and vapor barrier and which is metallized on the surface against the second film.

It has now been found that the combined metallization and varnishing results in a substantial and unexpected decrease in the permeability of the films, as can be seen from the experimental results presented below.

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Test 1

A biooriented film (A) having a thickness of 25 μm was prepared by extruding crystalline polypropylene consisting mainly of isotactic macromolecules obtained by stereospecifically polymerizing propylene and having a melt index of 4, the residue after extraction with heptane was 96, 5% and the ash content was 75 ppm. The resulting film was stretched both longitudinally and transversely. The film was then treated with continuous non-perforated 10a electrical discharges. Another film of the same strength (B) was made of high pressure polyethylene with a melt index of 2. The film was treated as above. The two films were combined with a polyurethane adhesive brushed at 1.5 g / m 2 and the composite film was passed through Vals-15 heated to 60 ° C. The oxygen permeability of the composite film was measured in this and subsequent experiments at 25 ° C according to ASTM standard D-1434.

Test 2

Layer A varnish over the other side of vinylideeniklo-20 chloride / akrylonitriilikopolymeerilakalla (molar ratio 80:20), which was coated with 1.5 g / m 2. The lacquered surface of film A was attached to film B as in Experiment 1. Oxygen permeability was measured as in Experiment.

Experiment 3 The second surface of film A was varnished with a mixture of polyvinyl alcohol and polyethyleneimine (weight ratio 80:20) applied at 0.8 g / m 2. The lacquered surface of film A was attached to film B as in Experiment 1.

Experiment 4 30 The other side of the film A was metallized in vacuo with aluminum until the surface resistivity was 3 ohms. The metallized surface of the film A was attached to the film B as in Experiment 1. The oxygen permeability of the combined films obtained in the experiments is shown in the following table, as well as the corresponding property of the films prepared in Examples 1 and 2 below (Experiment 5 and 6, respectively).

Membrane Oxygen permeability from the test cm3 / m2. 24 h. atm 51 1 500 2 60 3 120 4 50 5 2 10 6 2

The results of Experiments 2 and 3 show that the oxygen permeability is not satisfactory if the varnish alone is applied to non-metallized films. In contrast, the films of Experiments 5 and 15 6 are virtually oxygen impermeable, i.e., the oxygen permeability of the combined films of Examples 1 and 2 decreases sharply and unexpectedly compared to the high permeability of the films of Experiments 1-4 under the same experimental conditions.

In this context, it should further be noted that the permeability of the composite film has been considered to be calculable on the basis of the formula 1 / P = 1 / P + 1 / P2, etc., where P is the total permeability and PI, P2, etc. are the permeabilities of each layer. 25 permeability, see Techniche dell'Imballagio, N. 12, Dec.

1982, Anno XIII, p. 1094. Thus, the calculated oxygen permeability of the composite film according to Experiment 5 in the affidavit would be as follows: - permeability of the polyvinyl alcohol / polyethyleneimine mixture: 120 - permeability of the metallization layer: 50 - combination lP = 1/120 + l / 50-170 / 6000 <0.02833 The permeability P would thus be 35.3.

The calculated permeability of the composite film according to Experiment 6 would be as follows: 5 78641 - permeability of vinylidene chloride / acrylonitrile copolymer: 60 - permeability of metallization layer: 50 - combination: 1 / Ρ = 1/60 + 1/50 »110/3000« 0,0367 5 The permeability P was thus 27.3.

However, the final permeability of the combined films according to Experiments 5 and 6 (i.e. e.g. 1 and 2 of the application) is 2, i.e. considerably less than the calculated value. This clearly shows that a significant synergistic effect is achieved with metallization 10 and varnish. The metallization and use of the varnish now presented represents a new type of solution to the problem of protecting packaged products from the harmful effects of air. The combination according to the invention differs substantially from what has previously become known.

The oriented film is obtained by extruding and stretching polypropylene, which consists mainly of iso-tactical macromolecules and has a melt index of 0.5 to 5.

The second film may be a non-oriented film obtained by extruding polypropylene, polyethylene, crystalline propylene-ethylene copolymers containing mainly propylene and being either randomly of the segment type, polyethylene or polypropylene blended with each other or with a propylene-ethylene copolymer. or other polymers such as ethylene-vinyl acetate copolymers.

Additives known before film extrusion, such as opacifiers, stabilizers, lubricants, fillers, pigments, etc., can be added to the polymers, copolymers or polymer blends.

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Instead of an unoriented film, a bidirectionally oriented polypropylene film may also be used, provided that it is made by welding together, either by extrusion together or by coating.

The melt index of the polypropylene used in the preparation of the unoriented film is preferably 0.5 to 20, that of the polyethylene 0.5 to 15 and the ethylene-propylene copolymers 7 to 20,

The ethylene content of the copolymers is preferably 0.1% to 15% by weight.

The blends use polyethylene or copolymers from 1 to 50% by weight of the total weight of the blend.

The polyolefin films used in the present invention have a thickness of 10 to 10 μm. The lacquer acting as a gas or vapor barrier may be any polymer or copolymer and polymer blend having the required properties.

Particularly good results have been obtained using vinylidene copolymers containing more than 75% by weight of vinylidene-20 units or polymer blends based on polyvinyl alcohol having a medium or high degree of hydrolysis. Particularly suitable vinylidene copolymers include vinylidene chloride-acrylic-nitrile copolymers and vinylidene chloride-methyl methacrylate 25 copolymers. Polyvinyl alcohol-based blends that are particularly suitable include blends containing alkylene imine polymers such as polyethyleneimine, polypropylene ioline, and the like.

The lacquer layer may be applied to an oriented film 30 pretreated by continuous and non-perforated electrical discharges or by a flame or other method (e.g., chemical oxidation). Said varnish can also be applied to the unstretched film or to the film stretched in only one direction, in which case the stretching or stretching can be carried out before coating.

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The varnish can be applied equally to either surface of the polypropylene film or to both surfaces. The lacquer can be applied by known methods, using a polymer or copolymer dissolved or dispersed in water or an organic solvent, or a mixture thereof, by spraying, applying, dipping or the like. The total thickness of the lacquer layer may vary between 1 20yum,

The metallization is performed under reduced pressure either before or after lacquer-1Q with metals such as aluminum, zinc / gold, palladium or cadmium. If the metallization is carried out before varnishing, the film is preferably first treated with non-perforated electrical discharges, an oxidizing flame or chemical oxidation systems and then coated with a primer using known methods.

Metallization used for packaging purposes is done most conveniently and economically with aluminum.

The thickness of the metal layer is such that a surface resistance of 1-5 ohms is obtained.

A metallized film coated with a gas- and vapor-impermeable lacquer layer can optionally be printed using inks, and this printing can be done either before or after the lacquer.

Combined films are generally made by laminating two films together, either by placing an adhesive between the films or fixing without an adhesive, by passing the films between two rolls heated to a temperature of 30-90 ° C.

The bonding of two films without adhesives, as well as the coating of one film with one layer of heat-welded Yalla, can also be done using extrusion coating.

When adhesives are used, they are applied to other surfaces of the films by known methods, in particular by brushing, using solutions of adhesives or dispersing β 78641 in water or organic solvents. Hot melt can be used as adhesives. Generally, adhesive solutions with a concentration of 5 to 40% by weight are used, so that the amount of adhesive on the surface becomes 1 to 10 g / m.

Particularly suitable adhesives are synthetic adhesives formed from thermoplastic resins, such as cellulose esters and ethers, alkyl and acrylic esters, polyamides, polyurethanes, polyesters, or adhesives formed from thermosetting resins, such as epoxy resins, urea / formaldehyde, phenol / formaldehyde resins, melamine / formaldehyde resins, or adhesives made of synthetic rubbers.

In particular, carbon esters such as naphtha and toluene, esters such as ethyl acetate, or ketones such as acetone and methyl ethyl ketone were used as the adhesive solvents.

The composite films to which the invention relates are particularly well suited for food packaging, including the packaging of products under reduced pressure.

When the present invention is practiced, it may be extensively modified or modified: without departing from the spirit and scope of the invention.

The following examples illustrate the invention without limiting it

The,

In the examples:

Transmittance measurements were performed spectroscopically. Water vapor permeability was measured at 25 ° C according to A.STM E-96 standard.

Gas permeability was measured at 25 ° C according to ASTM-D-1434.

The SU index was determined according to ASTM D-1238-65T

30.

The weld strength of the composite films was measured by the so-called "peel strength test" method, in which the tensile strength of the weld was determined using an Instron-type dynamometer.

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The puncture resistance of the combined calyas was measured with an Instron type dynamometer using a tip with a diameter of 1.4 mm and a rim of 0.7 mm. Example l

The bidirectionally oriented film was prepared by 5 calyx extrusion of crystalline polypropylene consisting primarily of isotactic macromolecules prepared by stereospecifically polymerizing propylene with a melt index of 4, a heptane extraction residue of 96.5% and an ash content of 75 ppm, and stretched at 1 ppm. The film was first treated with continuous non-perforated electric discharges and then varnished with a mixture of polyvinyl alcohol / polyethylene'rimine (80:20, weight ratio) so that the basis weight of the 2 varnish layers became 0.8 g / m 2 and the metal was finally vacuum with aluminum until a surface resistance of 2 ohms was obtained.

The film (A) thus prepared had the following properties: ^ thickness 25 μm / 2 20 longitudinal breaking load 13 kg / mm 1 transverse breaking load 28 kg / mm T-longitudinal elongation 180% ^ transverse elongation 45% /. ^ tear strength (Elmendorf) 12 g / 25 μm: / 25 /

The second film (B) was prepared by pressing a film of LD polyethylene having a melt index of 2.

This film was treated with continuous non-hole-induced electrical discharges.

30 The above two films A and B were combined

Then by applying a polyurethane-2 adhesive to each other to a thickness of 1.5 q / m and passing the combined films to a temperature of at most 60 ° C between the heated rollers.

10

The combined film thus obtained had the following properties: * <* thickness 77yum τ transmittance 1% 3 2 o oxygen permeability 2 cm / m »24 h'atm 5 ^ carbon dioxide permeability 6 cm3 / ro1 * 24 h'atm t permeability 2 g / m1 * 24 h

- weldability range 115 - 125 ° C

«* · Weld strength 600 g / cm * - perforation strength 1200 g

1Q

Example 2

The procedure of Example 1 was otherwise followed, but a mixture of vinylidene chloride / acrylonitrile copolymer in a molar ratio of 80:20 was used as a lacquer surface for Kalyon A with a basis weight of 1.5 g / m 2.

Prior to varnishing, Kalyo is coated with a primer consisting of polyethyleneimine.

The composite film thus prepared had the following properties: 20 μm thickness 53 μm - «- transmit dance 1%; 3 o * oxygen permeability 2 cm / m .24 h »atm - carbon dioxide permeability 8 cm ^ / m ^ * 24 h-atm 2 - water permeability 1.5 g / m · 24 h

25 ^ weldability range 115-125 ° C

- weld strength 600 g / cm puncture resistance 1200 g

Example 3

The procedure of Example 1 was followed, but an unoriented film having a thickness of 25 μm and prepared by membrane extrusion of a crystalline ethylene / propylene random polymer containing 2.5% by weight of ethylene and a melt index of 12 was used before calibration. with 33 electric discharges that do not cause holes.

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The composite film thus prepared had the following properties: - thickness 52 μm τtransmit dance 1% 3 2 - oxygen permeability 2 cm / m · 24 In atm 5 τ- carbon dioxide permeability 6 cm3 / m2 * 24 h * atm τ water permeability 3 g / m2 , 24 h

τ weldability range 135 - 155 ° C

τ weld seam strength 650 g / cm τ puncture strength 1300 g 10 Example 4

According to Example 1, a combined pellet was prepared having the composition:

Kalyo Ά;

Bidirectionally oriented polypropylene film, 15.5 mm thick, treated with continuous non-perforated electrical discharges, printed with cellulose-based inks, primed with polyethyleneimine, 2 lacquered (basis weight 0.8 g / m) with a polyvinyl alcohol / polyethyleneimine mixture ( weight ratio 80:20) and finally 20 under reduced pressure with aluminum to a surface resistance of 2 ohms ·

Kalvo B; 25 .mu.m thick non-oriented film, made by extrusion of crystalline ethylene / propylene random copolymer containing 25% by weight of ethylene and having a melt index of 12, and treated with continuous non-puncture electric discharges before joining.

The composite film thus prepared had the following properties: 30 - thickness 54 μm T-transmittance 1% 3 2 T-oxygen permeability 15 cm / m · 24 h «atm carbon dioxide permeability 45 cm3 / m2 · 24 h * atm ~ water permeability 3 g / m3 · 24 h

35 h. Welding range 135 - 155 ° C

t weld strength 600 g / cm t perforation strength 1300 g 12 78641

Example 5

The film A> of Example 1 lacquered with a yinylidene chloride / acrylonitrile copolymer (molar ratio 8Q; 2Q) f was combined by the method of Example i into an unoriented film E having a thickness of 5 to 25 and prepared by film extrusion from crystalline ethylene / propylene. - a copolymer containing 2f 5% by weight of ethylene and having a melt index of 12.

The composite film thus prepared had the following properties: 10 ^ thickness 52 μm - transmittance 1 ^% 3 2 - oxygen permeability 2 cm / m .24 h «atm - carbon dioxide permeability 8 cm3 / m2 · 24 h * atm - permeability 1 g / m m · 24 h

15 h welding range 135 - 155 ° C

- weld seam strength 650 g / cm - hole thickness 1300 g

Example 6 2Q Non-oriented film B having a thickness of 50 μm and prepared by film extrusion of a crystalline ethylene / propylene random copolymer containing 2.5% by weight of ethylene and having a melt index of 12 was combined with Example 1. in a bidirectionally oriented film A prepared by film extrusion of polypropylene consisting mainly of iso-tactical macromolecules with a melt index of 4, a heptane extraction residue of 96.5% and an ash content of 75 ppm, under reduced pressure with aluminum (resistance 2 barley) and varnished by coating the metallized surface 2 to a basis weight of 0.8 g / m 2 with a polyvinyl alcohol / polyethyleneimine mixture (weight ratio 80; 20).

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The combined caly thus prepared had the following properties; ^ thickness 77 ^ ^ ^ transmittance 1% 3 o - oxygen permeability 1 cm / m · 24 h «atm 5 ^ carbon dioxide permeability 4 cm ^ / m2.24 h'atm 2 water permeability 2 g / m. 24 h

t · welding range 135 - 155 ° C

^ weld strength 700 g / cm r-puncture strength 1300 g 10 Example 7

Example 6 was repeated, but film A was lacquered on its coated surface with a vinylidene chloride / acrylonitrile copolymer (molar ratio 80:20) so that the surface pressures 2 became 1.5 g / m 2.

^ The properties of the combined film thus prepared were as follows: 'Thickness 77, μm -? transmittance l '% λ oxygen permeability 2 cm / m 24 h * atm 2Q t; carbon dioxide permeability 6 cm ^ / m2 · 24 h * atm 2 ^ water permeability 1 g / m · 24 h

^ weld range 135-155 ° C

^ weld strength 700 g / cm 25 ^ puncture strength 1300 g

Claims (3)

14 78641 A composite packaging film which is impermeable to gases and vapors and consists of two olefin polymer films, at least one of which is an oriented polypropylene film, the films being joined together with or without adhesive and the at least one film being coated with vinyl varnish and metallized with another from the contact surface, characterized in that the varnish consists of a vinylidene copolymer having a content of vinylidene units of more than 75% by weight or a polymer blend containing polyvinyl alcohol having a medium or high degree of hydrolysis. Film according to Claim 1, characterized in that the varnish consists of a vinylidene chloride / acrylonitrile copolymer or a vinylidene / methyl methacrylate copolymer. Film according to Claim 1, characterized in that the varnish consists of a polymer blend containing polyvinyl alcohol and a polyalkyleneimine, in particular polyethyleneimine or polypropyleneimine.